1. Field
Example embodiments relate to gallium nitride based (AlxInyGa1−x−yN, 0≦x+y<1) semiconductor devices and methods of manufacturing the same, and more particularly, to gallium nitride based semiconductor devices that simultaneously reduce damage and deformation of a wafer and enhance uniformity of wavelengths of emitted light by reducing a bow of the wafer, and methods of manufacturing the same.
2. Description of the Related Art
GaN materials may be used together with AlN and InN to generate light having relatively wide bands from ultraviolet rays to red spectrum regions, and have relatively high dielectric breakdown characteristics. Thus, GaN materials are widely used to manufacture relatively high power devices. However, GaN thin films are grown on heterogeneous substrates, e.g., sapphire, SiC and/or Si, due to absence of homogeneous substrates. As a result, many defects may occur on grown GaN thin films due to a mismatch in lattice constants between GaN thin films and heterogeneous substrates. Also, a bow of a wafer itself increases due to a mismatch in thermal expansion coefficients between GaN thin films and heterogeneous substrates. If the mismatch increases, cracks may occur in GaN thin films, or heterogeneous substrates may be broken.
For example, in a case where light emitting diodes (LEDs) including multiple quantum wells (MQWs) of an InGaN/GaN structure are formed on silicon substrates, templates used to grow MQWs need to have a defect density below 108/cm2 in order to manufacture relatively high brightness LEDs. For a defect density below 108/cm2, buffer layers and GaN thin films grown on silicon substrates need to have relatively great thicknesses. During growth of LED structures on silicon substrates, a compressive stress is applied in order to compensate for a tensile stress due to the mismatch in thermal expansion coefficients. In this regard, the applied compressive stress needs to be on the gigapascal (GPa) scale because buffer layers and GaN thin films have relatively great thicknesses. However, because silicon substrates become ductile at a relatively high temperature, such a relatively high temperature and relatively high compressive stress may cause a plastic deformation of silicon substrates. As a result, silicon substrates after being cooled may have relatively large bows in convex shapes and be hardened or broken.
Such a large bow of a substrate causes temperature non-uniformity during an MQW growth process, which causes a non-uniform composition of In in the MQW. Thus, wavelengths of light generated in the MQW are not uniform, which may deteriorate a yield of an LED. To solve this problem, a method of increasing a thickness of a substrate is generally used. However, an increase in a substrate thickness may raise the price of a substrate as well as may not completely prevent or reduce a plastic deformation of a silicon substrate at a relatively high temperature.